The selected IRRI germplasm (including 57 rice accessions from several countries) showed lower genetic diversity than that of the Thai commercial cultivars (improved and breeding lines) and Thai landraces. TheThai breeding lines had the highest genetic diversity while the IRRI breeding lines had the lowest. Interestingly, genetic diversity of Thai landraces was lower than that of Thai breeding lines, possibly because the Thai landraces were selected only from the North and the Central parts of the country, while the breeding lines were from all over Thailand